Taking the register

Until recently, SICK’s registration sensor portfolio has been led by the SICK KT5 sensor - probably the most commonly-used and depended-upon contrast sensor in industry worldwide. Now, a new breakthrough in registration performance, the KTS/KTX family is being officially launched in the UK at the PPMA Show in September 2017. David Hannaby, SICK’s UK Product Manager for Presence Detection, takes the opportunity to review registration sensing - a technology whose challenges and solutions should resonate with anyone using photo-electric devices in high-speed production today.

Next time you accept a sachet of sugar from a barista to sweeten your mocha, munch on your morning cornflakes, or reach for your bottle of shampoo, stop and take a closer look at the packaging. It may be cleverly hiding the tell-tale signs of decades of engineering development in a vital photo-electric technology.

Look closely, and you may see the tiny printed marks that are vital, precision-manufacturing instructions for labelling, printing or cutting machinery. In fact, almost any printed pack is likely to have them. Accuracy of registration is critical for FMCG manufacturers to eliminate wasted product and materials. Registration sensors are being constantly tested to cope with higher machine speeds, greater product batch changes and packaging design trends such as subtle colour differences, reflective foils and the use of transparent materials.

A bottle of shampoo could be transparent and/or reflective, making registration marks more difficult for a photo-electric sensor to detect. In automated electronics manufacture such as wafer cutting, or placing components on a printed circuit board for soldering, the consequences of inaccuracy could lead to product failure in use and even costly recalls.

Overcoming production challenges

Photo-electric registration sensing is based on the detection of differences in the amount of light returned to the sensor when a projected spot moves across a surface such as a package or a bottle. Technology development has seen the size of the spot decrease for improved resolution, the colour of the sender LEDs change for more reliable detection of marks and the intensity of light increased for better tone differentiation and greater speed of response to match production speeds.

Registration sensors need to be a class act to achieve consistently accurate detection rates, time after time - no matter what the challenges presented by the surface or substrate to be detected, or from the surrounding industrial environment.

With higher speed also comes the more exaggerated flutter of the materials being passed by the sensor, such as reel to reel material, or bottles on a filling line, so the substrate for the registration marks moves unpredictably.

The manufacturing conditions may be wet or dusty so that the sensor’s lens needs to compensate as it becomes coated and opaque, and background reflections from surrounding machinery can fool an inferior sensor into giving false signals.

The consistency in the light signal returned to the sensor could be affected by several factors, for example, an uneven, dirty or wet substrate material, minimal contrast differences between colours, when converted into gray scales by the sensor, matt black colours that absorb most of the light or highly-reflective finishes that divert the light away from the receiver.

Registration sensing options

The principal technology employed is contrast sensing, developed originally to detect the difference between black and white. Higher resolutions means that smaller marks can be detected, and improved algorithms and more intense light allow ever more subtle differences in gray scale tone to be distinguished.

Colour sensing detects a difference from a background colour to determine position for registration, for example, the blocks of colour incorporated into a logo. To achieve this, the sensor emitter/scanner set-up has to be tuned to particular colour frequencies and may use filters of specific colours to enhance the colour selected. Print and packaging are typical applications, but paint and wood finishes and even automotive components and textiles can benefit.

Luminescence sensors detect non-visible marks added with materials which can be made to fluoresce under UV light, for example adhesive. The marks can be placed on a label, pack or product without clashing with the ‘design aesthetic’ of the branding. Luminescence sensing can be particularly useful where transparency and clarity are a prerequisite of the package or substrate, such as see-through blister packs used for medical instruments or cosmetics.

Any photo-electric device is potentially susceptible to error from unwanted glare or reflections whether from the background environment, such as metal machinery surfaces, or even a white conveyor belt, glass screening or foil and reflective varnished print surfaces on a pack. Glare sensors can be used to overcome challenges and using careful set-up and advanced algorithms, the control system can be taught to disregarded incorrect messages from glare.

With advanced sensors that use SICK Delta-S technology, the glare problem is transformed into a solution by defining the boundary between reflection and non-reflection as a registration point. For example, in a pack design, an area of reflective varnished colour might border a matt white block where the sell by date and batch number are over-printed.

Industry 4.0-ready

The SICK KTS and KTX family of contrast sensors set a new benchmark in detection accuracy and switching frequency speed. SICK’s KT5 contrast sensors have long been an industry standard for detection of registration marks and customers now have the option of upgrading to the more compact KTS, for a space-saving solution, or to the KTX, which incorporates the new technology benefits into the same housing size as the KT5.

The KTS sensor reflects the trend towards miniaturisation common to photo-electric sensor development. Smaller and more compact sensors pack greater processing power into the confined spaces demanded by automated machine designs.

As Industry 4.0-ready sensors, the KTS and KTX also demonstrate the benefits of incorporating IO-Link connectivity. A key advantage of IO-Link enables quick and easy sensor teach-in and commissioning. When sensors need to be replaced, parameter settings can be easily downloaded from a PLC to a new sensor for rapid replacement and commissioning.

With new levels of detection accuracy and switching frequency speed, the KTS/KTX sensors offer flexibility in batch manufacturing, so product changes can be identified and new parameter settings automatically triggered with little or no interruption. More rapid and frequent production changeovers help manufacturers meet customer demands for product diversity, local or custom orders.

In Industry 4.0, the control system is fully connected to locate and ╥see╙ the sensor, so processes are given access to a full range of diagnostic capabilities not previously available. Through the combination of sensor self-monitoring and the ability to notify the control system precisely which sensor needs replacing, production teams have much greater flexibility in monitoring their processes.

By standardising on key product families such as the KTS/KTX, SICK is also ensuring wide applicability across different production process demands to reduce the need for large spares inventories.

The SICK KTS/KTX sensor

The SICK KTS/KTX family incorporates key features to meet the need of high-speed sheet and reel-fed production. With up to 70kHz switching frequency and down to 3╡sec jitter rate, the KTS and KTX are easily capable of coping with up to 250 packs per minute and compensating for high-speed flutter on reel-to-reel material edges.

Twin Eye Technology

SICK’s pioneering Twin-Eye Technology improves contrast detection with better depth of field and a wider sensing distance tolerance. The greater grey-scale sensitivity means even better sensing of monochrome or colour registration marks, even on high gloss packaging.

Conventional contrast sensors can struggle to perform reliably when faced with jittering webs, products with high-gloss surfaces, or where there is not much difference in contrast between a mark and its background. SICK has overcome these challenges by introducing a second receiving channel - a first for any contrast sensor - achieving better process stability and reducing the risk of machine downtime.

SICK’s Twin Eye Technology analyses the optically-split remission signal from the material surface and compensates for any noise pulses it contains, so stable and controlled switching is consistently achieved. As a result the KTS/KTX sensors have a significantly larger depth of field, as well as a sensing distance tolerance of ▒5mm, as-yet unique in contrast sensors of this type.

The KTS and KTX PRIME options enable fine contrast and colour differences to be detected using one device with a high degree of process reliability, while also blanking interfering colour gradients and imprints on the surface, or ‘noise’ from the detection background.

SICK - breaking new ground

The SICK KTS/KTX range of sensors is just one example of sensors breaking new ground in smarter sensing technology. Many of the production and detection challenges described are common to photo-electric solutions. By referring to a manufacturer like SICK, you can be confident of products developed with close customer collaboration that are ready to meet the needs of Industry 4.0.

To find out more about SICK registration sensor solutions and the new SICK KTS/KTX sensors, visit the SICK stand A26 at the PPMA show or visit the SICK website.